Identification of chief hydrocarbon source rocks based on n-alkane distribution patterns in western Qaidam Basin

The n-alkane distribution of crude oils from the western Qaidam Basin is characterized by even-to-odd (C₁₈—C₂₈) predominance. Source rocks from the region are mainly characterized by odd-to-even predominance. Based on n-alkane distribution pattern, combined with single molecule carbon isotope analysis, comparing crude oil with source rock, it was discussed in this paper the main source rocks in the western Qaidam Basin. The correlation of n-alkane distribution and single molecule carbon isotope analysis illustrated that the chief hydrocarbon source layer was E₂₃ and the secondary layers were E₁₊₂ and N₃₁ in deep region. Meanwhile, the chief hydrocarbon source layer was N₁ and the secondary layer was N₂ in shallow region. Hydrocarbon potential analysis showed that those samples with even-to-odd (C₁₈—C₂₈) predominance possessed higher TOC, bitumen "A", total hydrocarbon content and conversion ratio, displaying huge hydrocarbon generating potential.